Project Abstract Cognitive decline is nearly universal in older persons and its prevention is one of the most important public health challenges of the 21st century. Despite considerable progress in identifying the causes of cognitive decline in older persons, surprisingly little is known about the profile of healthy cognitive aging. Most of the available studies of healthy cognitive aging have examined cognitive change in persons without clinical dementia. However, the vast majority of persons without dementia who come to autopsy have extensive neuropathologic evidence of the diseases commonly known to cause cognitive impairment in old age, particularly Alzheimer's disease, cerebral infarcts, and Lewy bodies, and the exclusion of persons without clinical dementia does not account for the effect of accumulating neuropathology on the trajectory of cognitive aging. Moreover, most older persons exhibit a precipitous decline in cognition in the years just prior to death, a phenomenon referred to as terminal decline, and this also contributes to cognitive aging. Thus, a substantial portion of the cognitive decline currently attributed to healthy cognitive aging likely is due to the influence of accumulating neuropathology and terminal decline. We propose to use innovative statistical approaches to characterize the profile of healthy cognitive aging defined as age-related cognitive change not accounted for by the presence of common neuropathologies (i.e., Alzheimer's disease, cerebral infarcts, and the Lewy body diseases) or terminal decline. The proposed study will capitalize on the unique longitudinal cognitive and neuropathologic data available from two ongoing epidemiologic studies, the Religious Orders Study (P30AG10161), which will serve as the exploratory cohort, and the Rush Memory and Aging Project (R01AG17917), which will serve as the confirmatory cohort. These studies perform comparable and detailed annual cognitive evaluations on more than 2,300 persons in total, all of whom have agreed to brain donation. By the end of the funding period of the proposed study, more than 23,000 cognitive data points will be available from more than 2,500 persons with up to 20 years of annual follow-up. In addition, detailed post-mortem data will be available from more than 1,200 persons. Data from these studies will be used to model the trajectory of cognitive change as a function of accumulating neuropathology and terminal decline in order to elucidate the trajectory of healthy cognitive aging (i.e., age-related cognitive change not accounted for by common neuropathologies or terminal decline). The proposed study offers a novel, timely, and potentially powerful approach to identify the profile of healthy cognitive aging. Knowledge of the trajectory of healthy cognitive aging is essential for the identification of persons who might benefit from interventions to prevent age-related cognitive decline and, ultimately, for the identification of factors associated with successful aging.